Multi frequency feed system for high magnification cassegrain radiotelescopes at millimeter wavelengths

This paper presents the design of a feed system at K and Q frequency bands which permits simultaneous observation at a radio telescope. The system will be used for radio astronomical VLBI applications. With this design we get simultaneous operation with two different cryogenical receivers placed at the focal zone of the radio telescope with a relative pointing error lower than 3arcsec and an aperture efficiency higher than 75%. Quasi-optical techniques have been used to implement a frequency independent system. Phase corrected feeds have also been developed in order to reduce the size of the feeds and to allow cooling down and receiver noise temperature improvement. The design has been validated with laboratory test and on site tests after positioning and alignment at the focal zone of the 40 meter Yebes Observatory radio telescope.